1. The present invention is in the field of vapor phase epitaxial (VPE) growth of semiconductor layers on a semiconductor host substrate by a close-spaced technique in a demountable ampule while under super imposed pressure, and especially to the growth of highly volatile Group II-IV or Group III-V materials.
2. Description of the Prior Art.
Due to the relatively high vapor pressure of some elements, such as Hg, and the relationship of that fact to the techniques of forming HgCdTe, it has been found that the loss of Hg in the process has been a problem. Several methods of epitaxial growth of materials have been used. Investigations of the interdiffusion of HgTe and CdTe have led to the development of a close-spaced technique for the epitaxial growth of HgCdTe onto a CdTe substrate. The close-space technique of placing the growth source elements in close proximity to a substrate in an evacuated ampule and then sealing off the ampule under vacuum in preparation for the epitaxial growth. Each time a layer of the source material is deposited on the substrate, the ampule must be broken open and thrown away. If any subsequent layers need to be deposited on the substrate the substrate and source have to be placed in another evacuated and sealed ampule with the ampule later broken open to extract the substrate therefrom and thrown away. Obviously, this method is somewhat cumbersome, time consuming, and expensive. Teachings of this prior art method may be found in U.S. Pat. No. 3,472,685 or in an article entitled, "Growth and Properties of Hg.sub.1-x Cd.sub.x Te Epitaxial Layers", by O. N. Tufte and E. L. Stelzer in Journal of Applied Physics, Vol. 40, numbers 11, October 1969.
Some of the limitations and disadvantages of prior art close-space technology areas follows. New ampules must be made for each epitaxial growth and later broken to remove the growth. An ampule must be prepared for each separate step of the process, such as degreasing or other purification and for cleaning. The ampules must be sealed at high temperatures, thus releasing ampule impurities into the epitaxy environment. There can be no control of the atmosphere within the ampule after it is sealed, such as in situ cleanup of the ampule constituents during the epitaxial growth. The sealed ampule technique is not amenable to in situ multilayer growths and has a limitation to high volume production.
The present inventive method of close-space VPE growth under a high pressure environment of selected inert and reducing gases in a reusable demountable ampule alleviates all of the above problems.